A clamping device is known, applied to mixing machines, which allows to clamp a container containing a fluid product, for example paint, in a determinate position before the start of a cycle to mix the paint.
During this cycle, the mixing machine imposes a series of movements on the container, for example simultaneous rotations around one or more axes, oscillations along the longitudinal and transverse axes, or a combination of the movements, so as to mix the paint contained in the container.
The clamping device comprises a supporting plate, on which the container is rested, and a pressure plate, located at a determinate distance from the supporting plate and coaxial therewith. Both the plates are connected to a worm screw, or a rack device, made to rotate by an electric motor.
The direction of rotation of the screw, or the main gear of the rack, determines the reciprocal approach or distancing of the two plates and, consequently, the clamping or release of the container.
A command and control unit controls the electric motor and detects the quantity of current absorbed. This current is constant during the reciprocal approach and distancing of the plates, while it grows when the upper plate contacts the container, since the latter impedes the reciprocal approach of the plates.
A determinate increase in the quantity of current absorbed by the electric motor represents a corresponding increase in the pressure applied by the plates on the container, hence a relative clamping force applied to the container.
This device has a disadvantage, however, in that the current absorbed by the electric motor can have an irregular, unpredictable development, for example due to incrustations present on the thread of the worm screw and/or irregularities in the assembly or in the construction of the screws. Similar anomalies occur if a device with gears is used.
The above incrustations and/or frictions of other type are an obstacle to the movement of the clamping plates and can slow down their speed in the step of reciprocal approach. This prevents the correct determination of the clamping force which the said plates have to apply to the container.
Moreover, the above incrustations and/or frictions of other type can slow down and even block the reciprocal approach of the plates before the pressure plate actually contacts the surface of the container, with a consequent blockage of the electric motor, without the container being effectively clamped.
Starting the mixing cycle without the container being clamped with the correct and pre-set level of clamping force, or even without the container being clamped at all, can lead to very serious problems in the mixing cycle.
Another disadvantage is that, in known devices, the clamping force is pre-established at a given value, irrespective of the size, particularly the height, of the containers. This means that, for example, the pre-set value of the clamping force can be too low if the container is large, and can entail an ineffective clamping in the subsequent mixing cycle, or too high if the container is small, or made of plastic material, and possibly leading to the deformation of the container itself.
Clamping devices are also known which determine and memorize the height of the container, by means of a first approach of the pressure plate until it contacts the container. Subsequently, the pressure plate is distanced from the container by some millimeters, irrespective of the height of the container, and is subsequently returned in proximity with the latter until it contacts it again with a pre-determined force.
However, even in these conventional devices the clamping force is not determined automatically according to the actual detected height of the container, but is determined in advance, or set by the user.
One purpose of the present invention is to construct a clamping device, applied on a mixing machine, which automatically guarantees an effective and precise clamping of the container, at least according to the height of the latter and before the mixing cycle is started.
Another purpose is to be able to use the device with containers substantially of any size and/or material whatsoever, determining, at the start of the cycle and according to said size and material, the most suitable clamping force to ensure a correct clamping and prevent damage to the container.
The Applicant has devised, tested and embodied this invention to overcome the shortcomings of the state of the art and to obtain these and other purposes and advantages.